The basic goal of this investigation is to characterize the interaction between nocodazole and brain tubulin using physical techniques such as sedimentation and rapid kinetics. This research stems from the progress made in this laboratory showing that nocodazole interacts with tubulin and inhibits microtuble assembly. The basic molecular mechanism of this interaction is still not known although a conformational change was detected in tubulin upon binding of nocodazole. It is, therefore, proposed to: a) determine the binding of nocodazole and other derivatives of benzimidazole to tubulin by two techniques - namely, gel exclusion and sedimentation; b) establish the mechanism of nocodazole-tubulin interaction by kinetic studies using stopped-flow spectrophotometry; c) correlate the apparent specificity of nocodazole to the presence of tubulin polymorphism; and d) localize the sulfhydryl residues whose environments are pertubed upon forming a tubulin-nocodazole complex. The results from this investigation should yield information on the structure-function correlation of benzimidazole derivatives and on the effectiveness of these derivatives in utilizing the binding energy to achieve the inhibitory effect. Furthermore, the study on the apparent specificity of nocodazole may help to define the biological significance of tubulin polymorphism. The structural integrity of the sulfhydryl residues in tubulin is apparently important in microtubule assembly. The proposed study should help to define their roles in the reaction.